Many patients may have visual errors associated with the refractive properties of the eye such as nearsightedness, farsightedness and astigmatism. Astigmatism may occur when the corneal curvature is unequal in two or more directions. Nearsightedness can occur when light focuses before the retina, and farsightedness can occur with light refracted to a focus behind the retina.
There are numerous prior surgical approaches for reshaping the cornea. Over the years, surgical laser systems have replaced manual surgical tools in ophthalmic procedures. Indeed, with applications in a variety of different procedures, surgical laser systems have become ubiquitous in eye surgery. For instance, in the well-known procedure known as LASIK (laser-assisted in situ keratomileusis), a laser eye surgery system employing ultraviolet radiation is used for ablating and reshaping the anterior surface of the cornea to correct a refractive condition, such as myopia or hyperopia. Prior to ablation during LASIK, another surgical laser system employing a non-ultraviolet, ultra-short pulsed laser beam is used to incise the cornea to create a flap so as to expose an underlying portion of the corneal bed, which is then ablated and reshaped with ultraviolet laser beams from an excimer laser. Afterwards, the treated portion is covered with the corneal flap.
Laser eye surgery systems have also been developed for cataract procedures. These systems can be used for various surgical procedures, including for instance: (1) creating one or more incisions in the cornea, or in the limbus to reshape the cornea, (2) creating one or more incisions in the cornea to provide access for a cataract surgery instrument and/or to provide access for implantation of an intraocular lens, (3) incising the anterior lens capsule (anterior capsulotomy) to provide access for removing a cataractous lens, (4) segmenting and/or fragmenting a cataractous lens, and/or (5) incising the posterior lens capsule (posterior capsulotomy) for various cataract-related procedures.
For example, arcuate incisions are conical incisions made in the cornea. Typically, to prevent an incision from penetrating entirely through the cornea, an arcuate incision is made that does not penetrate the posterior surface of the cornea. Some laser eye surgery systems are capable of making intrastromal arcuate incisions by a laser where the incision is completely contained within the thickness of the cornea and does not penetrate the anterior or posterior surfaces of the cornea.
Typically, some form of imaging is used with laser cataract surgery systems to image and identify one or more surfaces of the eye. In some instances, it may be desirable to accurately identify, detect, and/or image various surfaces of the cornea before, during, or after surgery. For example, in some situations, it may be desirable to accurately determine a thickness of the cornea by imaging and/or by identifying an anterior and a posterior surface of the cornea. However, the cornea's birefringent characteristics may make the identification, detection, and/or imaging of the posterior surface of the corneal more difficult.
In other situations, an image of a proposed laser cut arcuate incision is overlaid on top of an imaged cornea for a surgeon to verify that the proposed incision does not penetrate the posterior surface of the cornea. If the incision is intrastromal, the surgeon also verifies that the proposed incision does not penetrate the anterior surface of the cornea. However, the image provided is typically just a cross-sectional image of the cut overlaid on the cornea, showing only one plane of the proposed incision. While the surgeon can verify that the proposed incision of the displayed cross-sectional plane is correct, he or she cannot verify that the incision is correct over the entire length of the proposed cut. Thus, laser surgery and imaging systems with improved characteristics to allow better imaging, detection, and treatment may be beneficial.